1. Field of the Invention
The present invention relates to a method and an apparatus for controlling an internal combustion engine having a function of eliminating minute particles in an exhaust gas. The method and apparatus according to the present invention can be applied to an internal combustion engine having a minute particle eliminating device which traps minute particles in an exhaust gas exhausted from an internal combustion engine of a vehicle and causes the trapped particles to combust, thereby purifying the exhaust gas.
2. Description of the Related Art
In order to trap minute particles such as carbon particles contained in an exhaust gas exhausted from an internal combustion engine, a minute particle trapping device incorporating a filter member comprising a ceramic honeycomb structure of a ceramic foamed member is usually used. In such a device, the air passing resistance of a filter is increased as minute particles are deposited on the filter member, resulting in decreased output. In addition, deposited minute particles degrade the filtering function. For this reason, minute particles deposited on the filter member are periodically removed to restore the function of the filter member of trapping the minute particles.
As a recovery means, a heating means is added to the filter member to heat and ignite the trapped particles, thereby removing them by combustion. When an electric heater is used as the heating means, this can simplify the apparatus. However, since the amount of heat output is small in comparison to that of a light-oil burner and the like, the filter member on which the minute particles are deposited is easily cooled by the exhaust gas flow under normal operating conditions, thereby preventing ignition of the minute particles, and even if ignited, the particles are soon extinguished by the exhaust gas flow.
As a means for improving the ignition property and to avoid quenching during combustion, a bypass flow path for communicating the upstream and downstream sides of the filter and a valve midway along the flow path are provided. In this filter recovery operation, the valve is opened and almost all of the exhaust gas is passed through the bypass flow path, thus considerably decreasing the flow rate of the gas passing through the filter (see, for example, Japanese Unexamined Utility Model Publication (Kokai) No. 58-9910). However, in this method, in addition to the filter, the bypass flow path, the valve, and a driving device for driving the valve must be provided, thereby complicating the system configuration, and rendering mounting of the system on a vehicle difficult.